Process of retanning leather with condensation products of phenols, amines, and formaldehyde



United States Patent 0.

PROCESS OF RETANNING LEATHER WITH CON- DENSATION PRODUCTS F PHENOLS, AMINES,

AND FORMALDEHYDE Martin Meister, Leverkusen, Gustav Mauthe, Opladen,

, and Kurt Faber, Koln-Stammheim, Germany, assignors to. 'Farbenfabriken Bayer Akfiengesellschaft, Leverkusen, Germany, a corporation ofGermany No Drawing. Application March 16,1954

Serial No. 416,713

- Claims priority, application Germany March 25, 1953 i 6 Claims. 01. 8-94.21)

The present invention relates to a new retaining process using cationic condensation products obtainable from monohydric phenols, amines and carbonyl compounds. In our copending application Ser. No. 366,612, now US. Patent No. 2,809,088, which was filed by Martin Meister andGustav Mauthe on July 7, 1953, there is described a process of retaining leather pretanned with organic or inorganic (mineral) tanning agents with salts of the condensation products of sulfones of monohydric phenols, non-aromatic amines and formaldehyde. The importance of this retanning process is based on the excellent fixation of these condensation products to leather pretanned with tanning agents containing synthetic sulfonic acid groups and/or vegetable tanning agents. The fast fixation of the retanning agents imparts to the leather a marked increase in weight (yield) and volume (thickness) and decreases the content of the substances capable of being washed out. The dyeability and absorptive powrfor fat of the leather thus retannedis substantiallyv improved, which is an additional favorable effect.

Inaccordance with the present invention we have found that, quite generally, cationic condensation products obtainable from monohydric phenols, amines and carbonyl compounds, Which do not possess markedtanning properties themselves, are excellently suited for re-' Patented June 9; 1959 invention, the treatment may be started at a pH within the range of about 3.5 to 4.5 and finished at a pH within the range of about 5 to 7.

The condensation products employed according to the invention are not tanning agents per so as are the products described in US. Patent No. 2,809,088, i.e. they cannot be used to prepare commercial leather from animal sides by the methods conventionally applied in tanning. In this respect, the herein described condensation products are distinguished from the products described in our copending application Ser. No. 295,558,

filed June 25, 1952, now US. Patent No. 2,733,977, which may also be used as tanning agents per se.

The hereindescribed cationic, phenolic condensation products show under certain conditions a more or less marked capacity for precipitating gelatine, which, however, is not nearly the same as that of the products described in our copending application Ser. No. 241,693, filed August 13, 1951. The capability of precipitating gelatine depends upon the proportion of the phenolic OH-groups or nuclei to the amino groups.

The two characteristic, principal properties of the condensation products used according to the invention, i.e., on the one hand, their more or less marked capacity of precipitating gelatine associated with a certain tanning capability, which is weak in water and more pronounced when the tanning process is carried out in alcohol, and, onthe other hand, the capacity of precipitating anionic compounds, for instance tanning agents and dyestuifs, account for the excellent properties of these products as retanning agents.

The condensation products employed according to the invention are by far superior to the fixing agents used at present in tanning processes, which are all of non-phenolic character. For instance, leather retanned with aniline' and chlorohydrate or hexamethylenetetraminethe fixing tanning leather and produce tanning effects equal to those obtained with the products according to our copending application Serial No. 354,656, filed May 12, 1953, and our U.S. Patent .N.0. 2,809,088.

rInstead ofmonohydric phenols, mixture'sof phenols and a preponderant proportion of .monohydric phenols may also be used in the production of the above-said condensation products. a

Suitable amines according to the invention are for, instance aromatic, aliphatic, and cyclo-aliphatic amines, which may be primary or secondary. As. carbonyl compounds there may be used ketones and aldehydes, especially formaldehyde. Condensation productsv of similar nature are described for instance in German Patents 644,- 708, 692,252 and 696,320. Furthermore, the soluble cationic compounds obtainable from a great many. of the long known, insoluble phenol resins by subsequent condensation with amines and aldehydes are suitable according to the invention.

These cationic phenolic condensation produ'cts are amphoteric in character, i.e. they form soluble'salts with acids and alkalies; they are insoluble around the isoelectric point.

. .Because'of their cationic nature these condensation products have a pronounced capacity for precipitatingpHnear the isoelectric point.

agents today most commonly used in tanning-shows an increase in weight of 6% (when 20% of fixing agent are used) whereas an increase in weight of 2025% is brought about by the retanning process using an equal quantity of the herein described cationic, phenolic condensation products. As already. mentioned above, another'advantage over the known fixing agents resides in the possibility of exhausting the tanning liquors com pletely by adjusting the hydrogen ion concentration to a This I neutralization step.

i cannot be adopted in the case of non-phenolic, cationic fixing agents, for instance aniline chlorohydrate, since the latter would thus be converted into free volatile aniline (poisonous effect). The weak tanning properties, which are due to the phenolic character of the new retanning agents, securea uniform penetration into 'the'hide and leather substance wherebypoor filling efiects are levelled up. Casehardening and similar clogging of the leather substance involved in the use of non-phenolic fixing agents do not occur 'when the hereindescribed condensation products are used; a i 1 v i We have further surprisingly found that a proportion of .up to 50% and more of the cationic tanning .agents described in our copending applications Ser. No. 241,693

' and Ser. No. 331,486 (now US. Patent No. 2,801,986,

filed January 15, 1953) can be replaced by the condensation products employed according to the invention, which have no satisfactory tanning properties as such and are primarily contemplated for'retanning purposes withoutad versely affecting the'tanning capacity of the mixtures, V

These mixtures are highly eflicienttanning agents and; excellent retanning agents; By-an appropriate choice'of the .quantities of the individualcomponents the astring-i encytofthe mixtures may be varied within .wide. limits;

i The invention is further illustrated by the following examples without being restricted thereto:

Example 1 A condensation product of phenol, formaldehyde and dimethylamine is obtained as follows: 900 parts of phenol moles) are condensed with 150 parts of formaldehyde (5 moles) (in form of a 40% aqueous solution) by addition of milliliters of a 25% aqueous hydrochloric acid during 4 hours at a temperature of 40 C. The excess of phenol is removed by steam distillation and thereafter the reaction product is washed neutral with water. Then it is dissolved in 1000 parts by volume of ethanol and treated with 300 parts by weight of 40% formaldehyde (10 moles) and thereafter while cooling 450 parts by weight of dimethyl amine (10 moles) are added. Addition of alcohol is continued, until a clear solution is obtained. The reaction mixture is slowly heated to boil so that the boiling point will be reached after about half an hour. The mixture is allowed to boil for further 2 hours, whereupon ethanol and water are removed by distillation. After cooling there is obtained a yellowish brownish transparent thick liquid, which may further be purified by washing it with water or by steam distillation. The product contains 9.1% of nitrogen, that means that one phenol radical contains about one dimethyl amine group. The resin is clearly soluble in diluted acetic acid as well as in medium concentrated alkaline lyes. It is soluble in most organic solvents. This condensation product is dissolved with hydrochloric acid until the solution shows a pH value of about 3.5 after adjusting a concentration of 25% (calculated on the dry substance).

This product is used for retanning goat skin pretanned with 25% by weight of pure tannin (mixture of equal parts of quebracho (1:0.5 sulfonated) and synthetic tanning agents), in the following manner: 100 parts of the Wet leather the thickness of which was ascertained precisely by measuring various spots thereof before retanning are milled in 200 parts by volume of water. parts of the above solution of the basic condensation product are added at intervals of minutes and the leather is milled in the solution for two hours. After this time the tanning solution has a pH value of about 4.3. By careful addition of ammonia (2.5%) the solution is brought to a pH of 6.2, the leather milled once more for 30 minutes and then removed. After this retanning process the leather shows a 25.7% increase in thickness. In comparison therewith, another leather pretanned in the same manner and retanned with a 25 pure tanning solution of quebracho (0.5 :1.0 sulfonated) shows a 5% increase in thickness. After drying a light brown colored, compact leather of good feel and good quality is obtained. This leather is essentially more compact than the said other leather (retanned with quebracho).

Example 2 N.N-dimethyl-p-hydroxybenzylan1ine is prepared by condensing phenol, formaldehyde and dimethylamine according to German Patent 92,309. A resin is prepared from the condensation products with formaldehyde according to German Patent 692,252, Example 3, wherein 10 parts of the aforementioned condensation product are mixed with 2 parts of 40% formaldehyde in an aqueous alkaline solution, and then heated for 7 hours at 60 C. Precipitation of the reaction product is prevented by addition of ethanol. After the reaction is completed the reaction mixture is distilled to remove lower distillable parts. There is obtained a slightly dark liquid oil which is easily soluble in diluted acids. This condensate dissolved in hydrochloric acid. This solution is brought to a dry content of 25 By retanning a goat skin with 20 parts of the 25% solution described in Example 1 and adjusting a pH value of 5.9 a leather is obtained which, in the wet state,

shows an increase in weight of 29.5% whereas the leather retanned with 5% of the pure tanning agent quebracho (0.5:l.0 sulfonated) increases in weight by 4.9%. After drying a very compact fine light colored leather of good feel and typical vegetable character is obtained.

Example 3 A condensation product is prepared according to German Patent 692,252 from 1 mol of 4.4'-dihydroxydiphenyldimethylmethane, 2 mols of dimethylamine and 2 mols of H 00. An alcoholic solution of 4.4'-dihydroxy diphenyl dimethyl methane is treated with 2 moles of formaldehyde and 2 moles of dimethyl amine. The mixture is allowed to stand for 48 hours in the cold, whereupon the product is soluble in diluted hydrochloric acid. The mixture then is boiled for 1 further hour under reflux (the reaction mixture then is precipitable by the addition of water and the precipitated oil is soluble in diluted hydrochloric acid, acetic acid or sulfuric acid). The excess of alcohol is removed by distillation and the reaction product then is dissolved in 10% of hydrochloric acid and furthermore condensed with 1 mole of formaldehyde for 7 hours on the steam bath. The reaction mixture shows no precipitate, but by the addition of ammonia the reaction product may be precipitated. The condensation is easily soluble in 2 N acetic acid. The resin obtained is dissolved in dilute hydrochloric acid to form a 25% solution. parts of the wet goat skin used in Example 1 are retanned with 20 parts of the 25% solution as described in Example 1 and brought to pH 6.4. After retanning the leather shows an increase in weight of 25.2%. After drying a very fine, compact leather is obtained, which has better filling properties and a better feel than leather retanned with 5 parts of a pure tanning agent in the form of quebracho (0.5: 1.0 sulfonated).

Example 4 A basic resin prepared from m-cresol, formaldehyde and morpholine according to German Patent 692,252 is dissolved in dilute acetic acid to a 25 solution.

100 parts of goat skin are retanned with 20 parts of this solution and the tanning liquors are brought to pH 6.0. The increase in thickness brought about by retanning amounts to 27.3%. The retanned leather is compact and has a good feel with a marked vegetable character.

.Example 5 A basic condensation product is prepared from p-cyclohexylphenol, diethylamine and formaldehyde according to German Patent 644,708, dissolved in dilute hydrochloric acid and the solution brought to a dry content of 25%. Proceeding according to the procedure of Example 1 of German Patent 644,708 the condensation product was prepared by reacting 17.5 grams of pcyclo hexyl phenol mol) with 33.3 grams of a 30% aqueous formaldehyde solution /s mol); this reaction mixture of phenol formaldehyde is then reacted with 36.5 grams of a 41% aqueous solution of dimethylamine /s mol) so that the molar ratio is /s:% or 1:2:2.

100 parts of the wet goat skin used in Example 1 are retanned with 20 parts of this solution as described in Example 1 and the tanning liquor is brought to pH 6.4.

The retanned leather shows an increase in thickness of 30.7%; it is compact and has a fine, pliable and mellow feel.

Example 6 2,2'-dihydroxy-5,'5-dimethyldiphenylmethane is prepared from p-cresol and formaldehyde according to the method described by Koebner (Zeitschrift fiir angewandte Chemie 46 (1933), page 251). 22.8 parts of this compound are mixed while stirring with 23.4 parts of a dimethylamine solution (38.6%), and 20 parts by volume of formaldehyde solution (30%) are added slowly by. drops at 60 C. The solution is condensed at 5100' C.

for about'29i hours. After cooling 25 parts of dilute hydrochloric acid (1:1). are added and the solution is broughtto a concentration of 25 by addition of water. 100Yparts of wet East Indian cabretta leather are retanned with parts of this 25 solution in 300 parts by volume of the tanning liquor as described in Example 1, the tanning solution being adjusted finally to pH 6.1. The dried leather shows a fine, light coloration, a compact feel and fine surface lustre. The increase in thickness brought about by retanning, which is measured in the dry state and referred to the thickness of the dry, non-retanned cabretta leather, amounts to 25.4%. Another cabretta leather, which was retanned for comparison with the retanning agent (10 parts of a 25% solution) described in Example 1a) of our copending application Ser. No. 354,656, shows an increase in thickness of 28% In similar manner a condensation product prepared from 2,2-dihydroxy-5,5-dimethyldiphenylmethane (228 parts), ethanolamine (13 parts) and formaldehyde solution of 30% strength (20 parts), which is dissolved in aqueous hydrochloric acid, may also be used for retanning leather. The leather thus retanned has similar filling properties and a similar good feel.

Example 7 10 parts of a trinuclear compound prepared from p-cresol and formaldehyde according to Koebner (Zeitschrift fiir angewandte Chemie 46 (1933), page 251) are condensed with 5.2 parts of a dimethylamine solution (38.6%) and 5.7 parts of formaldehyde solution (30%) at 80100 C. for 1% hours. The reaction product is dissolved with hydrochloric acid and brought to a concentration of 25 100 parts of wet East Indian cabretta leather is retanned with 10 parts of the above solution as described in Example 6. As compared with a non-retanned cabretta leather, the leather thus retanned has an essentially more compact and better feel.

In similar manner leather may be retanned with a condensation product prepared from 24.8 parts of the above-said trinuclear compound, 13 parts of ethanolamine and 20 parts of formaldehyde solution (30%), which is dissolved in hydrochloric acid. The leather thus obtained is still more compact than that retanned as described in the preceding paragraph.

Example 8 A phenol aldehyde resin is prepared by acid condensation of 100 parts of a mixture of technical phenol and cresol with '50 parts of formaldehyde (30%). 100 parts of the dry resin are dissolved in 100 parts by volume of 5N-sodium hydroxide solution and reacted with 35 parts of ethanolamine and 50 parts of formaldehyde solution (30%) successively. After the exothermic reaction is complete the mixture is heated to 100 C. for a further two hours. The reaction mixture is then poured into excess semi-concentrated hydrochloric acid (aqueous hydrochloric acid 1:-l), the precipitated resin separated and substantially liberated from the mother liquor by kneading. A solution of a dry content of 10% is prepared from the resin. By retanning 100 parts of wet East Indian cabretta leather with 25 parts of this solution and subsequently adjusting a pH of 5.9 a leather with a substantially more compact and better feel than a non-retanned leather is obtained.

Example 9 10 parts of the solution of the basic m-cresol resin employed in Example 4 are mixed with 10 parts of the solution of the basic dihydroxydiphenylsulfone resin in dilute hydrochloric acid (content of dry substance: 25 70), as it is obtained according to our copending application Ser. No. 354,656. 100 parts of wet goat skin prepared as described in Example 1 are retanned with 6 12 parts of this retanning mixture and the hydrogen ion concentration is adjustedto pH- 6.0. After drying at very compact leather with a fine surface lustre and an, agreeable feel is obtained. Another leather, which was retannedwith 3 parts of the pure tanningagent Sumac extract, has a substantially less compact feel.

Similar results are obtained by retanning East Indian cabretta leather with the above retanning mixture asdescribed in Example '6.

Example 10 A retanning mixture is prepared by mixing equal parts of the 25 solution of the basic resin described in Example 5 with the 25 solution of the tanning agent prepared from resorcinol, ammonium chloride and formaldehyde according to our copending application Ser. No. 241,693.

100 parts of a goat skin pretanned with vegetable and synthetic tanning agents are treated with 12 parts of this retanning agent. After adjusting a pH of 6 a fine leather of compact feel, which is similar to that of Example 9, is obtained. The increase in weight brought about by the retanning process amounts to 21%.

A leather of similar quality is obtained by carrying out the retanning process with a mixture of 70 parts of the 25% solution of the basic resin described in Example 6, first paragraph, and 30 parts of a 25 solution of the resorcinol tanning agent employed in Example 10.

Example 11 100 parts of a non-neutralized chrome calf leather, which was tanned in the usual manner with 3 parts of chromium oxide in the form of a commercial trivalent basic chromium salt, are retanned in about 200 parts by volume of water with 8 parts of the 25% retanning solution employed in Example 9 by adding the aqueous solution (1:2) in two portions at an interval of 10 minutes, milling for 30 minutes and increasing the pH value of the tanning liquor up to about 6.0 by adding, slowly and uniformly, dilute technical ammonia (1:10). The

. leather is removed after 10 minutes, shortly rinsed and finished as usual.

In similar manner the retanning substances and mixtures, described in the Examples l-10, may be used for retanning chrome leather.

The leather thus retanned has a markedly more compact feel than non-retanned chrome leather; it shows a good grain effect and a good dyeability without the chrome character being substantially affected as it is the case with typical semi-chrome leather,

We claim:

1. A retanning process which comprises retanning pretanned leather with an aqueous solution of an acidsoluble, cationic retanning agent obtained essentially from a condensation in an alkaline medium at a temperature up to about C. of ('l) a member of the group consisting of phenol, chlorophenol, cresol, 4,4- dihydroxydiphenyldimethylmethane, and cyclohexyl phenol (2) an amine having the formula HNR R wherein R is a member of the group consisting of hydrogen, lower alkyl, and hydroxy-lower alkyl, and R is a member of the group consisting of lower alkyl and morpholino, and (3) formaldehyde, 1-2 mols of the amine and from 1.5-2 mols of formaldehyde being employed per one mol of the phenolic compound, said retanning starting at a pH within the range of about 3.5 20 4.75 and finishing at a pH within the range of about 2. Retanning process of claim 1 wherein the condensation product is prepared from phenol, ethanolamine and formaldehyde.

'3. Retanning process of claim 1 in which the condensation product is prepared from cresol, ethanolamine, and formaldehyde.

4. Retanning process of claim 1 in which the com 2,890,095 1. densationproduct iszprepared from-.chlorophenol, ethanolamine,,and formaldehyde;

5. Retanning process of claim 1 in which the condensation product is prepared from phenol, dimethyl- 1312,5593 amine,.and formaldehyde.

'6. Retanning process of claim 1 in which the condensation product is prepared from cresol, dimethylamine, and formaldehyde.

8 References Cited inthe file ofthis patent- UNITED STATES PATENTS Pollak June 6, 1 933 Russell et a1; Feb. 27, 1940' Meister Feb. 7,1956 

1. A RETAINING PROCESS WHICH COMPRISING RETAINING PRETANNED LEATHER WITH AN AQUEOUS SOLUTION OF AN ACIDSOLUBLE,, CATIONIC RETAINING AGENT OBTAINED ESSENTIALLY FROM A CONDENSATION IN AN ALKALINE MEDIUM AT A TEMPERATURE UP TO ABOUT 100*C. OF (1) A MEMBER OF THE GROUP CONSISTING OF PHENOL, CHLOROPHENOL, CRESOL, 4,4''DIHYDROXYDIPHENYL - DIMETHYLMETHANE, AND CYCLOHEXYL PHENOL (2) AN AMINAE HAVING THE FORMULA HNR1R2 WHEREIN R1 IS A MEMBER OF THE GROUP CONSISTING OF HYDROGEN, LOWER LKYL, AND HYDROXY-LOWER ALKYL, AND IS A MEMBER OF THE GROUP CONSISTING OF LOWER ALKYL AND MORPHOLINO AND (3) FORMADEHYDE, 1-2 MOLS OF THE AMINE AND FROM 1,5-2MOLS OF FORMALDEHYDE BEING EMPOLYED PER ONE MOLE OF THE PHENOLIC COMPOUND, SAID RETAINING STARTING AT A PH WITHIN THE RANGE OF ABOUT 3.5 TO 4.5 AND FINISHING AT A PH WITHIN THE RANGE OF ABOUT 5 TO
 7. 